Fasteners, such as nut and bolt assemblies, are used in a wide variety of applications. The use of such assemblies has achieved wide acceptance due to their high reliability and relatively low cost as compared to other fastening means. However, some applications, such as joints in steam or gas turbines may expose the fastener assemblies to temperatures that exceed the fastener material's maximum allowable temperature, resulting in a reduced service life or failure of the fastener.
As the demand for higher efficiency turbines increases, the turbines are operated at higher temperatures exposing fasteners used within the turbines to higher temperatures. Continued exposure to these high temperatures may cause the fasteners to weaken and loose pre-stress. As the fasteners enter the creep range, the material properties begin to decrease exponentially leading to failure of the fastener. Rather than using fasteners made of more expensive materials, it is desirable to cool the fasteners in order to maintain the temperature of the fastener within the maximum allowable temperature of the material from which the fastener is made.
It is known to cool fasteners by passing a cooling fluid such as air or steam around a periphery of the fastener or through a cooling passage within the fastener. The effectiveness of such methods is limited by the heat transfer rate between the fastener and the cooling fluid. Hence, it is desirable to provide a cooled fastener assembly that facilitates or improves heat transfer from the fastener assembly to enable use of the fastener assembly in higher temperature applications.